SQL Server's Books on Line or T-SQL help documents have complete info on the parms of the sp_addtask stored procedure. The sp_addtask stored procedure can be found in the msdb database.
Replace the <userName> with that actual user name you want to monitor for a blocked state. It's only used in a description field in the msdb..systasks table here, so it will work as is, but puts a bogus description in msdb..systasks.
msdb..sp_addtask 'Block Monitor', 'TSQL', NULL, 'sa', 'admin', 1, 4, 1, 2, 10, 0, 0, 19980101, 19991231, 060000, 220000, 000000, 080000, 0, 'Bill Wunder', 0, 0, 'check_for_blocks', 2, 2, 'Check for Blocked <userName>'